The present invention generally relates to matrix materials for use in a wide variety of end use fields and applications. More particularly, the invention relates to self-repairing, settable or curable matrix material systems, containing reactive chemicals used in conjunction with release vessels or conduits such as fibers, the functions of which may be multiple.
Composites include at least two materials: the matrix and inclusions, such as reinforcement fibers or particles. Failures often occur at the interfaces between the matrix and fibers or particles. To prevent failure and fatigue, good bonding between the materials is needed. Numerous systems and techniques for repairing failed composites have been proposed.
Dry, a former professor at the University of Illinois, in several patents the invention for which she conceived and developed independently by 1990, e.g., U.S. Pat. Nos. 6,261,360, 5,989,334, 5,660,624, 5,575,841, and 5,561,173, described a cured matrix having a plurality of hollow release vessels, usually fibers, dispersed therein, the hollow fibers having a selectively releasable modifying agent contained therein, means for maintaining the modifying agent within the fibers until selectively released, and means for permitting selective release of the modifying agent from the hollow fibers into the matrix material in response to at least one predetermined external stimulus. The cured matrix materials have within them smart fibers capable of delivering repair agents into the matrix wherever and whenever they are needed.
In Dry's patents discussed above, damage was repaired by fibers containing modifying agent. Dry found that fibers, for retaining the chemical modifying agent, were easier to break than beads, they could cover damage which occurred over a larger area, could preserve strength of the structure, could act as a reservoir to retain larger volumes of agent therein than beads and, if the ends protruded, more chemical could be added.
Another researcher group, Professors Sottos, White and Moore at the University of Illinois, has made various attempts to provide self-healing composites starting in 1993, nearly 4 years after Dry's initial work. One design was to use a fairly expensive active chemical, such as dicyclopentadiene (DCPD) or Grubbs ruthenium in the matrix with dicyclopentadiene (DCPD) in beads. See, for example, U.S. Pat. No. 6,518,330. This approach, using very small beads and such a living chemical system, was designed to not require much force of damage but instead relied on small forces and predict a an automatic full reaction to pull the chemical out of the bead beads once the reaction has started. An article in Nature magazine by White, S., Sottos, N., et al., Autonomic Healing Polymer Composites, Feb. 15, 2001 describes this. However, the research group later discovered that the Grubbs ruthenium ruins the polymer matrix as described in. Their solution was to encapsulate the ruthenium; see U.S. Patent Publication No. 2005/0250878 A1, entitled “Wax particles for protection of activators, and multifunctional autonomically healing composite materials”. Their solution was to encapsulate the Grubbs ruthenium in wax in the matrix.
Subsequently, an elaborate system, called microfluidics, was developed by this group at the University of Illinois that included forming multiple layers of tubes, from a solidified ink which is then coated and the ink removed based on an ink developed at Sandia labs. The system includes in the matrix, a pump, valves in tubes to control chemical flow, and mixing towers to provide among other capabilities, composites with self-repair properties. See, for example, U.S. Patent Publication No. 2004/0226620 “Microcapillary networks”. See also, for example, FIG. 10, which schematically illustrates the self-repairing system with microfluidic aspects developed by University of Illinois. It requires a separate form piece for all the functions such as mixing towers, delivery tubes in all or most layers, a pump and valves to start and stop the flow in the tubes. The valves could be operated based on pH, and suggestions by others have been made to use light to modulate the valves.
U.S. Pat. No. 5,803,963 to Dry describes a self forming composite with an ongoing chemical reaction in which one chemical is released from a fiber into a mold containing two powders and that chemical reacts with one powder in the mold and in that reaction, a product is produced which reacts with the other powder in the mold. A polymer ceramic can be made in this way or other self forming composites.
U.S. Pat. No. 6,750,272, described a method for making a fiber-reinforced composite, the method including dispensing a reactive liquid into a mold, with the mold including fibers and a single-component activator on the fibers.
U.S. Patent Publication No. 2004/0007784 to Skipor et al., who worked with the White group at University of Illinois, describes a self-healing polymer composition containing a polymer media and a plurality of microcapsules or beads of flowable polymerizable material dispersed in the polymer media, where the microcapsules of flowable polymerizable material contain a flowable polymerizable material and have an outer surface upon which at least one polymerization agent is attached. The microcapsules supposedly are effective for rupturing with a failure of the polymeric media, and the flowable polymerizable material reacts with the polymerization agent when the polymerizable material makes contact with the polymerization agent upon rupture of the microcapsules. This is described as a way of making an initial cured form.
U.S. Pat. No. 6,858,660 to Scheifers et al. described a self-joining polymer composition, comprising a polymer, a plurality of amine pendant groups attached to the polymer and a plurality of microcapsules of flowable polymerizable material dispersed in the polymer where the microcapsules of flowable polymerizable material including microcapsules and flowable polymerizable material inside the microcapsules. The microcapsules are effective for rupturing with a failure of the polymer so the flowable polymerizable material cross-links with the reactable pendant groups upon rupture of the microcapsules.
Different techniques for formation of a composite structure are discussed in U.S. Patent Publication No. 2003/0119398 to Bogdanovich et al., where a resin distribution system and method for use in resin transfer molding includes using a 3-D orthogonal fiber structure having small channels therein for permitting a fluid to flow through the structure for formation of cured composites for use in such processes as resin transfer molding. The 3-D orthogonal fiber structure includes a woven system, having X-, Y-, and Z-direction fiber, each of having substantially no crimp within a body of the structure, thereby providing a system for distributing the fluid uniformly through the structure.
Other attempts have been made to provide self-repairing composites by other groups which used release from hollow fibers. See, for example, Motuku et al., from the University of Alabama, in “Parametric Studies on Self-Repairing Approaches for Resin Infused Composites Subjected to Low Velocity Impact”, Smart Material Structure 8 (1999) 623-638, studied low velocity impact response of glass fiber reinforced composites, which supposedly had the potential to self-repair both micro- and macro-damage. This University of Alabama group researched low velocity impacts for self-repair in fiberglass composites which were prepared at a fairly low temperature, sufficient to make fiberglass samples. Their studies focused on a two part system which needed, in general, mixing of more than one minute.
In the U.K., Bristol University researchers Ian Bond and Richard Trask used psuedoimpact and then heat to release and heat to cure self-repair agents in glass tube mats placed on or in composites, the technology suitable for use in a space environment. Still other tactics are described, for example, in “Bleeding Composites'—Damage Detection and Self-Repair using a Biomimetic Approach”, Pang et al., Composites: Part A 36 (2005) 183-1888.
Various matrix materials without separate chemical release inclusions, which are said to have self repairing properties, have been developed by numerous researchers; for example, studies have been ongoing by Professor Wutl of UCLA, at VPI and SU (Virginia Polytechnic Institute and State University), and at NASA Langely. Some of these developed systems are designed to reversibly repair damaged composites, but the materials are generally not strong enough for structural applications. One shortcoming is that many of the systems need heat to trigger the self-repair chemistry. Prof. Wutl suggests applications such as the glass in car headlights or heated windshields, where a heat source is readily available, for use of the self-repair system. The NASA system is used for ballistic damage where heat may be produced.
The subject of self-repairing composite materials not only includes concretes and polymeric materials, in addition to headlights and windshields, it has been suggested that housings and other parts of cell phones, computers and perhaps batteries could be made self-repairing. See, e.g., U.S. Patent Publication No. 2005/0027078 to Scheifers et al., which used chemistry to repair low energy damage such as in computer casings or cell phones by use of reactions which are self perpetuating. Other suggested self-repairing products include golf balls and tires.
The ideas for self-repairing composites are now widespread, but processing of the products under heat, development of adequate repair chemicals in terms of heat resistance, speed of repair, and simple systems which use an in-situ system of energy and chemical flow in a circulation system to repair well, systems to repair medium to high impact damage, multi-use applications, and applications to new end uses are all areas needing solutions and invention.